Centrifugal mercury switch



P 1963 R. HIPREWITT, JR

CENTRIFUGAL MERCURY SWITCH Filed Oct. 31, 1960 INVENTOR. RICHARD H. PREWITT, JR.

AGENT United States Patent 3,104,294 CENTRIFUGAL MERCURY SWITtJl-i Richard H. Prewitt, 3n, Swarthmore, Pa, assignor to Burroughs Corporation, Detroit, Mich, a corporation of Michigan 7 Filed Oct- 31, that), Ser. No. 66,161 Claims. (Cl. zed-so The invention hereinafter described and claimed has to do with electrical switches, but more particularly to those of the centrifugally responsive type effective to close electrical contacts at a pre-determined rotational speed.

More specifically the invention has to do with improvements in the centrifugally responsive switch described and claimed in applicants co-pending application entitled Electrical Switch, bearing Serial Number 46,227 and filed July 29, 1960.

The primary object of the present invention is to provide such a switch which is characterized by its simplified construction lending itself to mass production with marked economies in cost.

More specifically it is an object of the invention to provide such a cent-rifugally responsive switch relying upon the novel arrangement of its parts and the surface tension of an electrically conductive fluid, such as mercury, to prevent closure of its switch contacts under all conditions other than when subjected to a predetermined rotational speed about its own axis.

In accordance with the above objects and first briefly described, the invention comprises a housing having a cylindrical cavity which contains a predetermined quantity of electrically conductive fluid, preferably mercury, and which has a plurality of electrical contact elements preferably spaced equally about and within the walls of the housing with portions thereof extending within a restricted peripheral groove formed in the cylindrical walls of the cavity. The groove cooperates with the surface tension of the electrically conductive fluid to prevent the fluid from entering the groove to interconnect the contact elements except under a predetermined centrifugal force established by rotation of the housing about its own axis. The spacing of the contact elements is so related to the quantity of mercury within the cavity that in any rest position of the housing the quantity of mercury is insuflicient to bridge any two of the contact elements. This is also true when the housing is subjected to any force except that centrifugal force which is equal to or more than the predetermined centrifugal force at which the switch is designed to be actuated. Thus the construction of the switch is such as to prevent closure of its switch contact element except under the desired condition.

In the drawings:

FIG. 1 is a perspective view of a switch embodying the preferred form of the present invention;

FIG. 2 is a transverse sectional view through the wall of the housing looking downwardly from a position over a switch and showing its interior construction, the spacing of the contact elements around the walls thereof and a pool of mercury resting on its bottom wall;

FIG. 3 is an elevational view of the switch as it would appear when resting on its cylindrical side wall and with parts broken away to show the condition of the pool of mercury when the switch is in this position;

FIG. 4 is a view taken along the line 44 of REG. 2 and as if FIG. 2 were not in section; and

FIG. 5 is a view similar to FIG. 4 but taken along the line 5-5 of FIG. 2 and showing the mercury in its condition under the influence of sufiicient centrifugal force to bridge and thus electrically interconnect the contact elements of the switch.

I 3,ltt,2st Patented Sept. 17, 1963 "ice More specifically and with detailed reference to the drawings illustrating the preferred embodiment of the invention, it is seen that the switch comprises a housing Iii of suitable electrically non-conductive material, including a cup-shaped base member 11 and a cap or cover member 12 telescopically joined and tightly secured together as by screws 13. The base member 11, as seen in FIG. 4, is formed with upstanding cylindrical walls 14 and a flat bottom wall 15, the latter having a peripheral flange 16 extending beyond the walls 14-. The bottom wall 15 is provided in its upper surface with a plurality of grooves 17 which, as seen in FIG. 2, extend radially from the axis 18 of the switch housing.

The cover or cap member 12 includes a flat top wall 19 and a depending cylindrical wall 20, the last mentioned wall being telescopically received over the cylindrical wall 1t of the base member 11 to rest on the top surface of the flange 16 in a manner to form a tightly sealed enclosed cylindrical cavity 21 within the housing. In the condition shown in FIG. 4 it will be seen that when so assembled the construction of the base member 11 and the cover 12 is such as to provide a peripheral groove 22 extending completely about the side walls of the cavity. It will be understood that the groove has a vertical dimension forming a restrictive passageway leading to electrical contact elements or pins 23 extending through the cover member 12 with their inner ends terminating in the groove 22 at a point spaced away from the entrance to the groove. The other ends of the contact pins extend outwardly of the cover 12 to provide for interconnection to associated apparatus or circuitry. It will also be seen that the inner cylindrical wall surfaces of both the base member 11 and the cover 12 are provided with peripheral offsets 24 and 25 respectively adjacent the groove 22, the purpose of which will be explained hereinafter.

Prior to assembling the cover member 12 upon the base member 11, a predetermined quantity of electrically conductive fluid 26, in the present case mercury, is placed in the base member 111. The quantity of the mercury is predetermined in accordance with the desired centrifugal force at which the switch is to be actuated. It is understood that the dimensions controlling the rpm. rate at which con-tact closure occurs are those of the cavity 21, the recess 22 and the quantity of mercury 26.

As mentioned in the above-identified co-pending application of applicant, the switch is adapted for use in a wide range of apparatus. However, it is not believed necessary to amplify this aspect of the invention in the present case. The important aspect of its use is its rotation about the axis 18.

in its operation, rotational speed imparted to the switch will cause the mercury first to climb up and to spread evenly around the cylindrical walls of the cavity 21, as seen in FIG. 5, and within the recess formed by the peripheral offset portions 2 4 and 25 of the housing members 11 and 12. The dimension of the groove 22 is such that the mercury will be prevented by its own surface tension from entering the groove until the housing reaches the rotational speed at which it is desired to interconnect the contact elements 23. Thus the restricted dimensions of the groove cooperate with the surface tension of the mercury to prevent closure of the contacts until the switch reaches the predetermined rotational speed. When the desired rotational speed is reached, the surface tension will be overcome and the mercury will flow into the groove thus to eflect electrical interconnection of the con tact elements 23. The air within the recess will escape around the mercury to re-enter the cavity 21 thus permitting the mercury to flow into the recess to make electrical contact between the pins 23.

, a a 3 It may be important that the switch not be closed under conditions other than the predetermined rotational speeds selected.

In FIG. 3 it is seen'that the pool of mercury 26" is insufiicient to bridge adjacent pins. Thus'it is understood that if the switch or the apparatus to which it is attached is dropped or otherwise subjected to a shock of sufiicient force to cause the mercury to flow into the groove, no two of the contacts would be bridged by the mercury. In some circumstances it might be desirable that the single contact pin s be replaced by pairs or other multiples and such is contemplated by the invention.

To provide for quick response in the movement of the mercury to the outer walls of the cavity 21 and to overcome its inertia, the radial grooves 17 have been provided in the wall of the base member 11.. These grooves will grip the mercury and cause it to spin simule taneously'with the start of rotation of the switch housing,

making the switch instantly responsive to such rotation.

From the above description it is seen that the invention provides a foolproof centrifugally responsive switch that ductive contact elements positioned within the walls of said housing with portions thereof extending from the housing and other portions located in a restrictive'groove formed about the periphery of the cylindrical walls of the cavity and providing open communication with the interior of the housing, and a pool of electrically conductive fluid within said cavity, said fluid being of insufii cient quantity to bridge said contacts except when the housing-is subjected to a predetermined centrifugal force drical wall substantially midway between the end walls and of restrictive capillary dimensions, a plurality of electrically conductive contact elements spaced around and within said cylindrical walls with portions thereof extending exteriorly of the said walls for interconnection with associated apparatus and other portions extending into said groove which is in open communication with the interior of said housing, and a pool of mercury within said housing, said mercury being of a quantity sufficient only in response to a pre-determined centrifugal force generated by rotation of said housing about its axis to bridge and interconnect said contact elements by flowing into said groove. I

4. A centrifugally responsive switch comprising a housing of electrically non-conductive material and including a cylindrical side wall having an axis, and end walls closing the ends of said cylindrical wall, three electrically conductive contact elements equally spaced around and teriorly of said wall for interconnection with associated apparatus, and other portions extending into a radially extending peripheral groove of capillary dimensions formed about said cylindrical wall substantially midway between said end walls, said peripheral groove providing open communication with the interior of said housing, and a pool of mercury within said housing, said mercury being of a quantity sufficient only in response to a predetermined centrifugal force generated by rotation of the housing about its axis to spread itself around the cylindrical walls and into the peripheral groove in said cylindrical wall thus to bridge and interconnect said contact 7 elements.

5. A centrifugally responsive switch comprising a housing of electrically non-conductive material, said housing generated by rotation thereof about the axis of the cylinmidway between the end walls and of restricted capillary dimensions, a plurality of electrically conductive contact elements spaced around and within said cylindrical walls with portions thereof extending exteriorly of the said walls for interconnection with associated apparatus and other portions extending into said recess which is in open communication with the interior of said housing, and a pool of electrically conductive fluid within said housing,

said fluid having a surface tension and being of' a quantity sufficient only in response to a pre-determine-d centrifugal force generated by rotation of the housing about itsaxis to bridge and interconnect said contact elements by flowing into said recess.

3; A centrifugally responsive switch comprising a housing of electrically non-conductive material and including a cylindrical side wall and opposite end walls forming a completely enclosed cylindrical cavity within the houscomprising a cup-shaped base member and a complementary shaped cover member telescopically interfitted to form a completely enclosed cylindrically shaped cavity having top and bottom walls and an axis, the dimensions and construction of said housing-forming members being such that when so assembled a groove is provided about the cylindrical periphery of the cavity midway between the top and bottom walls and of restrictive capillary dimensions, electrically conductive contact elements spaced around the axis'of said housing and extending through one of said housing-members with portions extending from the housing for interconnection with associated apparatus and other portions extending within said groove spaced from the cylindrical wall of said cavity, and a pool of ing, a groove formedaboutthe periphery of said cylin- References Cited in the file of this patent UNITED STATES PATENTS 1,031,893 Volk L July 9', 1912 1,412,228 Andersen et al. Apr. 11, 1922 2,164,991 Ingres July 4, 1939 Von Bomhard Dec. 22, 1959 FOREIGN PATENTS 213,735 -Germany V Y Sept. 22, 1909 

1. A CENTRIFUGALLY RESPONSIVE SWITCH COMPRISING A HOUSING OF ELECTRICALLY NON-CONDUCTIVE MATERIAL HAVING AN ENCLOSED CYLINDRICAL CAVITY, A PLURALITY OF ELECTRICALLY CONDUCTIVE CONTACT ELEMENTS POSITIONED WITHIN THE WALLS OF SAID HOUSING WITH PORTIONS THEREOF EXTENDING FROM THE HOUSING AND OTHER PORTIONS LOCATED IN A RESTRICTIVE GROOVE FORMED ABOUT THE PERIPHERY OF THE CYLINDRICAL WALLS OF THE CAVITY AND PROVIDING OPEN COMMUNICATION WITH THE INTERIOR OF THE HOUSING, AND A POOL OF ELECTRICALLY CONDUCTIVE FLUID WITHIN SAID CAVITY, SAID FLUID BEING OF INSUFFICIENT QUANTITY TO BRIDGE SAID CONTACTS EXCEPT WHEN THE HOUSING IS SUBJECTED TO A PREDETERMINED CENTRIFUGAL FORCE GENERATED BY ROTATION THEREOF ABOUT THE AXIS OF THE CYLINDRICAL CAVITY. 